Two comparative blue emitting InGaN/GaN multiple quantum well (MQW) structures, for lighting and laser diode
applications, with and without pre-strained layer, were grown by MOCVD. Temperature dependent photoluminescence
(TDPL) and time-resolved (TR) PL were used to study their optical and transient properties. PL signals from InGaN
MQWs were divided into two parts: one is the band to band transition of InGaN; the other is the broad defect band. It is
indicated that the InGaN/GaN MQW structure with prestrained layer has larger activation energy. TRPL measurements
were performed in 10-300 K and with the detection wavelength cross over the emission peak. It is found that the MQW
sample with prestrained layer has deeper localization depth. Temperature dependence of PL decay time shows an
interesting behavior of an increase from 10K to 30K and then a decrease till 300K.
This paper presents a new method of designing binary optical structures to improve light extraction efficiency for
emitters. Using this method a novel binary optical structure is generated. Such structures with an approximate width of
300 nm, are non-period and small enough in size so that they do not generate diffraction orders other than the zero order.
They are also insensitive to polarization. They serve as an antireflection layer, sending light outward that would
otherwise be absorbed within the device.
The experimental devices were GaN based LEDs emitting at 460nm. The non-periodic binary structures and some
periodic structures such as triangle-lattice Photonic Crystals (PC), 12-fold Quasi-periodic Photonic Crystals (QPC) are
fabricated on the same sapphire side of a LED's flip chip with a Focus Ion Beam (FIB) for comparison. The surface
profile of the structures was analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM).
Near field scanning optical microscopy (NSOM) was used to measure the output spectral properties of the devices.
Electrical Luminescence (EL) measurements show that the greatest enhancement of emission light intensity was
achieved in non-periodic binary structures. This increase was 60~135% at room temperature. It demonstrates that this
Non-Periodic Binary Optical Structures will be useful for fabricating high efficient GaN-based LED.